The invention relates to improvements in methods of and in apparatus for applying flowable adhesives to running strips or webs of paper or the like. More particularly, the invention relates to improvements in methods and in apparatus which can be resorted to with advantage in connection with the application of adhesive to running strips or webs (hereinafter called webs for short) of wrapping material of the type utilized in connection with the making and processing of smokers' products.
Examples of webs of wrapping material which must be provided with layers or films of special adhesive and/or with layers or films containing different types of adhesive are those which are employed for the assembly of filter rod sections with plain cigarettes to form filter cigarettes of unit length or multiple unit length. Wrapping material of such character is known as tipping paper and is utilized in machines known as filter cigarette makers or tipping machines. Examples of such machines are those known worldwise as MAX (distributed by the assignee of the present application). A MAX machine is designed to assemble successive groups of co-axial plain cigarettes and filter rod sections of unit length or multiple unit length, to connect the constituents of such groups with each other by resorting to so-called uniting bands (sections of a web of tipping paper one side of which carries a continuous or composite film of adhesive) which are convoluted around the filter rod sections and the adjacent end portions of plain cigarettes, and to thereafter sever the groups to obtain filter cigarettes of unit length.
German patent No. 24 45 342 C2 discloses a machine which can change the quantity of adhesive being applied to successive still coherent uniting bands of tipping paper, i.e., prior to separation of successive foremost uniting bands from the leader of a running web of tipping paper. The quantity of adhesive per uniting band is changed by reducing or increasing the thickness of the film of applied adhesive and/or by changing the area(s) of the adhesive-coated portion(s) of each uniting band. The purpose of changing the quantity of adhesive per uniting band is to properly relate the quantity of applied adhesive to the permeability of the web of tipping paper and/or to properly relate the quantity of adhesive to the force with which certain portions of a uniting band must adhere to the filter mouthpiece, to the plain cigarette and/or both. The patented machine is further provided with means for intermittently interrupting the application of adhesive to the running web of tipping paper. This is accomplished by resorting to a rotary cam the RPM of which is related to the speed of the running web of tipping paper and which serves to alternatingly move the running web toward and away from the adhesive applying nozzle.
The patented apparatus exhibits certain drawbacks, especially as far as its versatility is concerned. For example, the patented apparatus applies adhesive to those portions of the running web which are not to be bonded to constituents of filter cigarettes. Furthermore, the patented apparatus increases the rate of application of adhesive immediately subsequent to each interruption of transfer of adhesive to the running web of tipping paper.
The aforementioned German patent also discloses a method of applying adhesive to a running web of tipping paper. The method involves the utilization of at least one nozzle with an orifice which discharges adhesive into contact with the running web of tipping paper. The method does not take into consideration the possibility of injury to a smoker, e.g., when the filter cigarette is smoked all the way to the end of the tobacco-containing part (i.e., to the end of the plain cigarette forming part of the filter cigarette). Combustion of the inner end of the tobacco-containing part of the filter cigarette can result in the development of flame (due to combustion of adhesive which forms part of the adhesive coat on the inner side of the convoluted uniting band), and such flame can cause injury to and can frighten the smoker. Moreover, once the tobacco-containing part of a filter cigarette is combusted close or very close to the end portion which is surrounded by the respective terminal portion of the convoluted uniting band, the glowing remaining part of the tobacco-containing portion is likely to fall to the floor or onto a chair or table or suit or dress with resulting damage to the carpet, to the piece of furniture or to the clothing and the danger of fire.
A further drawback of the patented method and apparatus is that the accuracy and predictability of the application of adhesive decrease when a tipping machine turns out filter cigarettes at a rate which can be achieved by resorting to modern high-speed tipping machines. This results in the making of a high percentage of rejects as well as in customer complaints.